HLS: Add factory for Extractors

[IanDBird]

In ExoPlayer v2, the HlsMediaChunk class is responsible for constructing what extractor is required for a given format (createExtractor). This means that HLS handling is tightly coupled to what extractors are used.

Since applications are capable of creating their own extractors (e.g. their own TsExtractor) it would be useful to allow these to be passed into the HLS implementation to be used. This would require the HlsMediaSource accepting an extractor factory which could then be created by the application.

[stari4ek]

this is the only way to bypass FLAG_ALLOW_NON_IDR_KEYFRAMES, FLAG_DETECT_ACCESS_UNITS which can be required for some HLS streams.
HlsMediaChunk does not provide any other easy way to extend. It's final and pretty complex to provide own variant

[AquilesCanta]

Please give it a try and let us know if it works for you.